Currently, there is no FDA approved therapeutic antibody capable of depleting long-lived plasma cells. A plasma cell-specific monoclonal antibody could be used to treat plasma cell malignancies (multiple myelomas), which are fatal and for which there is no effective treatment, and antibody-mediated autoimmune and severe allergic disease (e.g., systemic lupus erythematosus and asthma). Immunoglobulin (Ig)-based monoclonal antibodies that recognize plasma cell surface antigens, such as CD138 and CD38, are being evaluated for plasma cell targeting; however, these antigens are expressed by many other cell types, which complicates plasma cell targeting and creates the potential for side effects. NovAb's scientific founders discovered that primitive jawless fish, lampreys and hagfish, use highly diverse leucine-rich repeat (LRR)-based antibodies called Variable Lymphocyte Receptors (VLRs) for antigen recognition, instead of the Ig-based antibodies used by all higher vertebrates. Due to the vast evolutionary distance between humans and lampreys (~500 million years), highly conserved human proteins and carbohydrates that are invisible to mammalian immune systems because of self-tolerance, are likely to be immunogenic in lampreys. Capitalizing on the lack of tolerance to mammalian antigens and the unique structural features of the lamprey VLR antibodies, NovAb has developed VLR monoclonal antibodies specific for novel plasma cell-restricted antigens in humans and non-human primates. However, the plasma cell-specific VLR antibodies will need to be engineered before they can be used therapeutically. Because VLR antibodies will be seen as foreign antigens by the mammalian immune system in their native form, we propose to make humanized variants using human LRR receptors as scaffolds to limit immunogenicity. We will also construct VLR chimeric proteins to allow them to interface with effector mechanisms of the human immune system, such as Fc receptors and complement pathways, to facilitate the depletion of target cells.